LEDs, especially high-power LEDs, have been subject to rapid development in recent years, in particular the light yield produced as a function of a predetermined control signal has sharply increased. White LEDs have now become so mature that they can be used in the automotive industry as a light source for the front headlights.
For motor vehicle manufacturers it is important to be able to guarantee that these LEDs can be replaced, for replacing defective LED for example. In such cases account must be taken of the fact that the development of LEDs is advancing all the time, that future LEDs can already provide the respective light power needed with smaller activation currents and that the brightness of a headlight should match before and after the LEDs have been exchanged.
It is already known that the number of LEDs can be combined into one or more LED modules or LED arrays in a headlight in order to provide the light power required in each case. Future LED arrays are likely to require fewer LEDs in order to generate the light power needed.
Furthermore it is already known that the light power radiated from an LED light source can be detected by means of a sensor system and the control current for the LED light source can be increased as a function of the output signals of this sensor system, in order for example to counter an ageing-related power reduction of the LED light source.
An automatic headlight regulating device for a motor vehicle is known from DE 102 42 864 A1 with a least one headlight featuring at least one light source. This regulating device is connected to an evaluation of electronics coupled to sensors and to control electronics adjusting at least one of a number of light distributions of the light source. These control electronics regulate the light distribution of the light source as a function of a command of the evaluation of electronics. At least one of the sensors is embodied as at least one light emitting diode assigned to the headlight for measuring the brightness of incident light.
A lighting device provided in particular for motor vehicles is known from DE 102 48 238 A1. This lighting device contains a diode arrangement comprising a number of light emitting diodes and a scattering disk or the like which lets through part of the light emitted by the light emitting diode arrangement and reflects part back to the light emitting diode arrangement. The light emitting diode arrangement is assigned to a control and/or evaluation unit. The diodes of the light emitting diode arrangement can be activated by this unit so that a respective diode is driven alternately as a light emitting diode and as a photodiode. In this case in each phase at least one diode respectively is driven as a light emitting diode and at least one diode as a photodiode. The output signal of the respective diode driven as a photodiode is fed to the control and or evaluation unit.
A motor vehicle lighting module is known from DE 103 13 24 6 A1. This features individual LEDs as lighting means, a basic chassis for retaining the LEDs, a sensor for detecting outer and/or inner influences during operation of the LEDs and/or manufacturing-technology-related characteristics of the LEDs, a data memory for the detected data and electronics for controlling and regulating the LEDs as a function of the detected influences and/or characteristics.
A sensor device, a use of a sensor device and a motor vehicle light are known from DE 10 2004 038 422 B3. This sensor device features a least one transmission unit arranged inside a sensor carrier and at least one receiver unit assigned to the transmitter unit arranged inside the sensor body as well as a test surface arranged between the transmitter unit and a receiver unit. The transmitter unit and/or the receiver unit are embodied from a molded part with an inserted radiation transmitter and/or the radiation receiver. The test surface is formed by an exit surface of the transmitter unit and an entry surface of the receiver unit.
A multifunction light sensor for a motor vehicle is known from EP-B1-0 910 525, which is intended for detection of a plurality of ambient conditions of the motor vehicle. The output signals of the sensor are used to control devices of the motor vehicle, for example the windows, the sliding roof, a ventilator or the screen washer of the motor vehicle. These are controlled with a periodic control signal of a predetermined frequency. The light emitted by the LED light source is evaluated using a phase-sensitive amplifier in accordance with the lock-in method.